![\"\"](\"http://www.mathskey.com/userfiles/image/steps_images/step1.JPG\")
Observe the table, define the x coordinate is depth (km) and y coordinate is temperature(oC).
\Find the temperature of a rock, that is 10 km below the surface, so x = 10.
\Substitute x = 10 in equation y = 35x + 20.
\y = 35(10) + 20
\y = 350 + 20 (Multiply: ![\"\"](\"/test/fckeditor/editor/plugins/fckeditor_wiris/integration/showimage.php?formula=446826f578c7c48d7fa6cb94ef848bdb.png\")
)
y = 370 (Add: 350 + 20 = 370)![\"\"](\"http://www.mathskey.com/userfiles/image/steps_images/solution.JPG\")
The temperatute of a rock is 370oC.